Thousands of Victorian parents will be forced to make alternative arrangements for their children today as a 24-hour teachers' strike shuts more than 100 schools and severely disrupts many others.

In what is expected to be one of the largest education strikes in recent years, more than 30,000 teachers from more than 2000 government and Catholic schools will take unprecedented joint action this morning over wages and working conditions.

According to union figures issued at 4.30pm yesterday, about 90 Catholic schools and 85 government schools will be unable to offer any classes, forcing parents to make alternative arrangements for their children.

The State Government has urged principals to consider taking in students from other schools.

The teachers' strike is the second in Victoria in less than six months. Last September about 20,000 teachers walked off the job and about 110 schools and preschools closed as part of a national day of action.

The teachers' action came as Victoria's 26,000 nurses also warned of statewide industrial action next month if the State Government proceeded with plans to scrap the nurse/patient ratio system.

The Education Department said it believed only about 20 schools would be closed today - well under union estimates.

But some principals said there appeared to be more support among staff for today's action than the previous strike, amid growing frustration over the lack of progress on salary and working conditions.

"I think it's the most heartfelt stopwork I've seen in a long while," said Sydenham-Hillside Primary School principal Peter Devereux. "Very few of my staff went out last time, but I think teachers view this is as a significant issue and they are very concerned about what's happened."

The Australian Education Union is demanding a wage rise of 30 per cent over three years, reduced class sizes, less contract employment and more resources to attract and retain teachers in the face of a looming shortage. Catholic teachers, who are represented by the Victorian Independent Education Union but rarely engage in stopwork action, want parity with the government system rises.

The Government has offered an increase of 9 per cent over three years, which includes 2.25 per cent dependent on productivity improvements. It has also proposed that teachers cut one week off their annual leave or teach summer classes in exchange for a new wage deal.

Premier Steve Bracks warned that the dispute could go on for months, saying the Government could not afford to pay teachers an extra 30 per cent and continue to invest in schools and hospitals. "We won't cave in," he said. "We'll get a fair outcome and we'll have a better education system."

But AEU state branch president Mary Bluett said the Government had been given a log of claims 14 months ago, and teachers were fed up.

At Melbourne Girls College, principal Judy Crowe said 52 teachers would be on strike today and all students except those in year 7 had been asked to stay home.

Roxburgh College principal Bob McFarlane said the senior college would have to close, while the junior school would offer year 7 programs only.

Genazzano FCJ College in Kew would continue as usual, while at Marcellin College, almost half the teachers were involved in the stopwork, but programs had been reorganised to allow all classes to continue except year 11, said principal Mark Merry.

Susan Hughes, executive officer of the Victorian Parents Council, said many parents supported more pay for teachers, but "a lot just wish that there had been another way, and in some people's eyes, the strike doesn't reflect well on teachers as professionals".

Jacinta Cashen, a parent and president of the Victorian Council of School Organisations, said she would stay home to look after her two primary school-aged children, as well as her niece and a friend's child.

Deb Taylor said her partner had organised a day of leave to take care of her two young sons while she fulfilled study commitments. "That will probably have to come out of his pay," she said.

Parents Victoria president Gail McHardy warned that some parents may have to leave their children at home.

Opposition Leader Robert Doyle said the Government could prevent the strike by applying to the Industrial Relations Commission to end the protected bargaining period during which workers can legally strike.